Polystyrene foam is bulky due to its foamy and lightweight, and moreover polystyrene foam has a strong structure and hence internal gas cannot be compressed or discharged even by the application of considerable external pressure. The efficiency of transporting recovered waste polystyrene foam is thus poor, and transportation costs and treatment costs are very high.
Methods for reducing the volume of waste polystyrene foam has been proposed, wherein waste polystyrene foam is made to contact a liquid medium in which polystyrene foam is soluble, thus dissolving the waste polystyrene foam and reducing the volume thereof (Japanese Unexamined Patent Publication No. 1990-1748, Japanese Unexamined Patent Publication No. 1993-59212, Japanese Unexamined Patent Publication No. 1995-113089, etc.). Furthermore, a solvent that is relatively safe during use, can be easily handled, has no toxic irritating or unpleasant odor, is safe, does not require use of gas or deodorant masks or local ventilation, helps to improve the working environment and promote safety, and thus cause no problems for the working environment, causes no nervous or liver disorders, and is not teratogenic or carcinogenic has been developed (Japanese Unexamined Patent Publication No. 2002-60535).
However, polystyrene resin treated with the solvent disclosed in Japanese Unexamined Patent Publication No. 2002-60535 and other solvents of prior arts exhibit excessively strong adhesion, causing it to adhere to the treatment vessel and become ropy when removed therefrom, which complicates the removal of the polystyrene resin from the vessel.
When polystyrene resin is immersed in a solvent to reduce its volume, the polystyrene resin generally absorbs the solvent and forms a gel. The gel then sediments, forming a two-layered structure (with the solvent in the upper layer and the gel in the lower layer) inside the treatment vessel. If the polystyrene resin absorbs a large amount of solvent when it forms a gel, the amount of the solvent remaining in the dipping vessel decreases and the addition of further solvent may be necessary to reduce the volume of additional polystyrene resin. Therefore, it is economically advantageous to have a smaller amount of solvent absorbed by the polystyrene resin when it forms a gel.
Furthermore, if the polystyrene resin absorbs a large amount of solvent, the resulting gel becomes sticky and adheres to the dipping vessel, and the removal of the gel from the dipping vessel becomes complicated. Therefore, it is desirable for the treated polystyrene resin (gel) to exhibit only a small degree of adhesion to the dipping vessel.
Because polystyrene resin has a density less than that of solvents, polystyrene resin floats when placed in a solvent; however, the greater the area over which the polystyrene resin contacts the solvent, the greater the volume of the polystyrene resin is reduced. Therefore, after placing the polystyrene resin in the solvent, the floating polystyrene resin is press fit by pushing it with a presser board, etc., to maximize the area over which the polystyrene resin contacts the solvent. However, if the polystyrene resin whose volume is to be reduced is rigid, a large force is needed for press fitting, and therefore it is advantageous if the polystyrene resin whose volume is to be reduced is soft to some degree. Therefore, it is desirable that the solvent be able to form the polystyrene resin into a gel. However, caution is required if the polystyrene resin is excessively softened by the solvent because, as described above, the adhesion of the polystyrene resin to the vessel generally increases.
In other words, if the treated polystyrene resin is insufficiently hard, the adhesion thereof to the vessel or presser board is too great and this lowers operating efficiency, and if the treated polystyrene resin is too hard, the pressure required for press fitting increases. Therefore, it is desirable that a solvent that gives the treated polystyrene resin a preferable hardness be provided. Furthermore, because many types of polystyrene resin will float in solvents, simply placing the polystyrene resin in a solvent is disadvantageous with regard to the treatment time since the contact area between the polystyrene resin and the solvent will be small. Therefore, it is more effective to apply pressure to the polystyrene resin floating in the solvent (e.g., by placing a heavy substance on the polystyrene resin) to dip the polystyrene resin into the solvent. In this case, if the adhesion of the treated polystyrene resin is too strong, in many cases, the polystyrene resin will adhere to the object that is used to apply pressure to the polystyrene resin, complicating the operation. Therefore, development of a solvent that reduces the adhesion of polystyrene resin that is treated therewith has been awaited.
When the volume of polystyrene resin is reduced in supermarkets, etc., which collect polystyrene foam items such as food trays, etc., equipment or the like for strictly controlling temperature should be made as unnecessary as possible. Therefore, development of a solvent that can reduce the volume of polystyrene foam even when the ambient air temperature is 0° C. or less in winter has been awaited.
The present invention provides a solvent for treating polystyrene resin so that the adhesion of the treated polystyrene resin is lower than that treated by heretofore-used solvents, with the amount of absorbed solvent being small and able to reduce the volume of polystyrene resin even at low temperatures, and a method for treating polystyrene resin using the solvent.